1. Field of the Invention
The present invention relates to a sustained release coating composition and a preparation coated therewith, and more particularly to a sustained release coating composition containing a higher alcohol and a metallic soap, as well as to a sustained release coated preparation obtained by coating a core material, which contains an amino acid, vitamin, carbohydrate, antibiotic, antibacterial substance, steroid, anthelmintic or the like as its principal ingredient, with the coating composition.
2. Discussion of the Background
It is well known that coatings are applied to drugs in order to improve the appearance of the resulting pharmaceutical products, and therefore to increase the value of the drugs as commercial goods. Developments which have come about include the application of coatings to mask the unpleasant tastes, odors and the like of pharmaceutical products and/or to facilitate the administration of such pharmaceutical products. Further developments in the coating of drugs has been directed to the application of coatings to stabilize pharmaceutical products or to adjust and control the development of their efficacy as drugs. Moreover, coatings have found utility, for example, in the production of enteric preparations, sustained release preparations, repeat action type preparations and so on.
Not many methods, however, have been proposed with the objective of applying coatings to powders on an industrial scale. Although the known atomizer coating method makes use of a higher fatty acid or glycerin-fatty acid ester as a coating material (see, Japanese patent publication No. 13192/1975) and, other coating methods such as the roll coating method and micro-encapsulation method have been used to coat powders, none of these methods are satisfactory.
Coated preparations are generally required to have not only prompt release properties, in view of the stability of drugs, but also long-lasting release properties from the standpoint of adjustment and control of development of the efficacy of the drugs. Release patterns have been designed by taking these two requirements into parallel consideration. In fact, some coated preparations have been produced under conditions which take into account these two release patterns.
Although the conventional atomizer coating method is advantageous from the standpoint of production costs, it is accompanied by such drawbacks that the release patterns of the resulting coated preparations are constant and the preparations suffer from poor release properties when glycerine-fatty acid esters such as hydrogenated oil are employed as coating materials. Another factor is that limitations are imposed on applicable drugs when higher fatty acids are used as coating materials, because such higher fatty acids are reactive to basic drugs. Attempts have also been made to accelerate the release velocities of drug preparations by incorporating a surfactant such as sucrose-fatty acid ester or propylene glycol-fatty acid ester into the coating formulations with a view toward making improvements in the release properties of such coated drugs (see, Japanese patent publication No. 48050/1982; Japanese patent Laid-Open No. 28441/1984). However, the methods of release which are based upon release control of core materials by the action of surfactants are accompanied by several shortcomings which include the following: (1) Although surfactants having high HLBs are desirable from the viewpoint of release velocities, surfactants may, in many instances, fail to form homogeneous melts with coating materials such as oils and/or fats and tend to separate from the coating materials unless they have low HLBs. (2) Although it is desired that the coating materials which are employed in the atomizer coating method have certain degrees of melting readiness, for example, melting points on the order of 50-80.degree. C., from the viewpoint of work efficiency and the storage of coated preparations, the addition of surfactants results in the reduction of the melting points of the coating materials or in the formation of coating films having reduced strength. (3) The amount of surfactant which is added to the coating formulation must be limited to such low levels that no significant improvement in release velocity is expected.
On the other hand, the coating materials which are required in the roll coating method, the micro-encapsulation method and the like, such as cellulose acetate phthalate, ethylcellulose, polyvinylacetal diethyl aminoacetate, are costly. Furthermore, these methods require the use of an organic solvent during production of the preparations and are thus troublesome to carry out. All of these factors just discussed increase the coats of production. A need therefore continues to exist for improved coating formulations for drug preparations.